Antenna device

Abstract

An earth configuration achieving easy installment without deteriorating performance of an antenna device. The antenna device has a balanced antenna element, a shield plate arranged between the balanced antenna element and a conductor of a car, and a supporting member, and the shield plate blocks electrical coupling of the conductor from the balanced antenna element when the antenna device is mounted on the body of the car.

What is claimed is: 
     
       1. An antenna device comprising: a loop shaped antenna element to receive GPS signals;   an antenna member to block electrical coupling of a conductor of an external apparatus with said loop shaped antenna element; and   a supporting member to support said antenna member at a predetermined distance from said loop shaped antenna element to isolate said supporting member from said loop shaped antenna element,   wherein the conductor is a conductor in an instrument panel of a vehicle,   said antenna member is arranged between said loop shaped antenna element and the conductor when an assembly of said antenna device is mounted inside of the instrument panel,   the assembly of said antenna device is fixed inside of the instrument panel via a fitting member to fix said antenna member so that said antenna member is below said loop shaped antenna element and above the conductor, and   said loop shaped antenna element includes two lead wires are respectively connected to a navigation apparatus via a feeder cable, and said antenna device and the navigation apparatus are separately arranged inside of the instrument panel.   
     
     
       2. The antenna device according to claim 1, wherein said antenna member has a plate conductor member provided independent of said loop shaped antenna element. 
     
     
       3. The antenna device according to claim 1, wherein, when the assembly of said antenna device is mounted inside of the instrument panel, said antenna member is fixed to the fitting member and the fitting member is fixed to a metal portion of the vehicle to ground the antenna member. 
     
     
       4. The antenna device according to claim 2, wherein an effective area of said plate conductor member perpendicular to the direction toward the external apparatus from said plate conductor member is greater than an effective area of said loop shaped antenna element perpendicular to the direction. 
     
     
       5. The antenna device according to claim 2, wherein said supporting member is filled between said loop shaped antenna element and said plate conductor member with insulating material. 
     
     
       6. The antenna device according to claim 2, wherein said supporting member supports said plate conductor member and said loop shaped antenna element so as to be substantially parallel to each other. 
     
     
       7. The antenna device according to claim 2, wherein said plate conductor member is metal plate. 
     
     
       8. The antenna device according to claim 2, wherein said plate conductor member is formed by a metal net. 
     
     
       9. The antenna device according to claim 8, wherein each mesh of the metal net is designed smaller than about one-tenth of wavelength λ of a radio wave of interest. 
     
     
       10. The antenna device according to claim 2, wherein an effective area of said plate conductor member is set larger than 9λ 2  /64 when wavelength of a radio wave of interest is λ. 
     
     
       11. The antenna device according to claim 2, wherein said plate conductor member has a rectangular shape whose sides are equal or longer than 3λ/8. 
     
     
       12. The antenna device according to claim 11, wherein said plate conductor member is a square. 
     
     
       13. The antenna device according to claim 1, wherein said antenna member has a conductor member having function of blocking electrical coupling, and said fitting member fixes said antenna member so that said conductor member is isolated from the conductor in the instrument panel. 
     
     
       14. The antenna device according to claim 1, wherein said fitting member is an adhesive layer. 
     
     
       15. The antenna device according to claim 1, wherein, when a wavelength of a radio wave to be received is λ, said supporting member supports said antenna member at a distance between λ/25 and λ/2 from said loop shaped antenna element. 
     
     
       16. The antenna device according to claim 1, wherein the assembly of said antenna device is mounted inside of the instrument panel by fixing said fitting member to said antenna member.